Modular wireless fixed network for wide-area metering data collection and meter module apparatus

ABSTRACT

A scalable and modular fixed-base wireless network system for wide-area metering data collection, composed of at least one of each of the following components: meter modules, which monitor, store, encode and periodically transmit metering data via radio signals (air messages). The network may contain both one-way (transmit only) and two-way (transmit and receive) meter modules; Receiver Base Stations, which receive, decode, store and forward metering data to a central database and metering data gateway, referred to here as the Data Operation Center (DOC). Base Stations do not perform any meter data processing, but simply transfer decoded air messages to the DOC; and a Data Operations Center, which communicates with all of the network&#39;s Base Stations and receives decoded air messages from the Base Stations. The DOC processes, validates and stores metering data in a meter database that it maintains for the entire meter population operating in the network. The DOC has the capability to export or forward metering data to other systems via standard data protocols, which may be scaled up in its air message handling capacity and in its application features, by integrating it with a wireless data-forwarding (downlink) channel, such as a paging network, which is required in order to provide service to two-way meter modules that may be operating in the network. This channel enables the sending of time synchronization and other commands to two-way meter modules, thus providing the operator with considerable flexibility in their choice of network capacity, features and system cost.

A one-way direct sequence spread spectrum (DSSS) communicationswide-area network is used as the data collection channel (uplink) of anautomatic meter reading (AMR) application and a paging network, or othersuitable downlink network, is used as an optional forward (downlink)channel in a cost-effective manner. The network is simple to deploy,highly scalable and modular. It offers a wide range of service options,from basic daily meter readings to advanced applications based oninterval consumption data, to full two-way applications, while keepingthe system's deployment and ongoing costs proportional to the serviceoptions and capacity requirements selected for various segments of themeter population. A high-output-power meter module is introduced, whichprovides significant benefits when operating on the network.

FIELD OF THE INVENTION

The present invention generally relates to wireless messaging systemsand methods. In particular, the present invention relates to wirelessmessaging systems and methods for automated meter reading (AMR) andmetering data collection.

BACKGROUND

Automated Meter Reading (AMR) started out as a more efficient andaccurate method for utility metering data collection, compared to manualmeter reading of electric, gas and water meters. Several importantadvantages of AMR over manual meter reading helped develop it into aspecialized branch of the data communications and telemetry industry.Worth noting among these advantages are the reliability, accuracy andregular availability of metering data, collected from hard-to-reachmeter locations as well as from standard meter locations; highercustomer security (no need to enter homes) and satisfaction (accuratebills); and reduced cost of customer service call center and servicehouse calls for settling billing disputes.

Various technologies are implemented in AMR. All implementations performthe tasks of interfacing the meter in order to sense consumption,communicating consumption data to a central site and storing consumptiondata in a computer system at the central site. Wireless technologieshave be. the most common in AMR system implementation due to the ease ofthe installation process and, in many cases, the low initial andoperating costs of the system.

Among wireless implementations of AMR, a categorization has beenestablished between mobile data collection systems and fixed-base datacollection systems, or networks. Fixed network systems have someimportant distinctive advantages, brought about by the frequent(typically at least daily) consumption data collection, in comparisonwith mobile systems, which merely provide a more reliable method ofcollecting monthly meter reads for billing purposes. Worth noting amongthese advantages are: flexibility of billing date; marketing tools suchas time-of-use (TOU) rates, demand analysis and load profiling, whichenable clearer market segmentation and more accurate forecasts forutility resource generation, and also serve the goal of energyconservation and efficient consumption; and maintenance tools such asimmediate notification of utility resource leakage or of accountdelinquency. These advantages have triggered increased interest andcommercial activity regarding fixed network data collection systems forutilities, particularly utilities in regions undergoing deregulation ofutility services.

Several methods and systems for implementing fixed-base data collectionfrom a plurality of remote devices, such as utility meters, to a centrallocation, have been developed and introduced in the past years. Acategorization has evolved as the AMR industry developed, generallydifferentiating between one-way and two-way wireless data networks. Somesystems, such as those described in U.S. Pat. No. 5,438,329 toGastouniotis et al., U.S. Pat. No. 5,883,886 to Eaton et al. and U.S.Pat. No. 6,246,677 to Nap et al., require that each meter module on thenetwork be a two-way module, i.e. contain a receiver circuit in themeter module. Although two-way communication features such as on-demandmeter reading and other remote commands for meter configuration andcontrol are generally desirable, they may not be required for the entiremeter population of a utility. Since the inclusion of a receiver in themeter module contributes significant cost to the module, it would bemost desirable to allow a utility service company the flexibility todeploy an AMR network, which may contain and support both one-way andtwo-way meter modules.

U.S. Pat. No. 5,963,146 and No. 6,172,616 to Johnson et al., assigned toItron, Inc. of Spokane, Wash. (referred to henceforth as the Itronnetwork) and U.S. Pat. No. 6,163,276 to Irving et al. and U.S. Pat. No.6,195,018 to Ragle et al. (referred to henceforth as the CellNetnetwork) describe data collection networks that may also operate asone-way (collection only) data networks. These networks support thelarge volume of data, expected by advanced metering applications, bydeploying intermediate data collection nodes (Remote Cell Nodes, orRCN's, in Itron's network and Microcell Controllers in CellNet'snetwork), each of which creates a small data collection cell with ashort-range RF link and a typical service population of several hundredsof meters. In these networks, the data collection nodes receive messagesfrom meter modules, perform metering data analysis and extract, orgenerate, specific meter function values to be transmitted to the nextlevel in the network hierarchy. The wide-area network connecting theintermediate level and the higher level is typically a wireless networkoperating on an additional, licensed, RF channel, in order to avoidinterference. This configuration, which distributes the ‘networkintelligence’ among many data collection nodes, serves the purpose ofreducing the data flow into the central database when a large amount ofmeters is analyzed for load profile or interval consumption data. Italso serves the purpose of reducing air-message traffic between theintermediate node and the higher-level concentrator node, referred to asIDT (Intermediate Data Terminal) in the Itron network and Cellmaster inthe CellNet network.

However, the configuration of the Itron and CellNet networks becomesinefficient in the common case where only a part, or none, of the meterpopulation requires advanced metering services like TOU rates, whilebasic daily metering service is required for the whole meter population.This inefficiency is imposed by the short-range radio link between themeters and the data collection nodes, which significantly limits thenumber of meters a node can serve, regardless of how many meters requireor do not require to be read frequently for interval consumption data.That way, an expensive infrastructure of up to thousands of datacollection nodes may be deployed, which may often consist of plenty ofunused excess capacity. A more efficient network would therefore bedesirable, in order to reduce basic equipment cost, as well asinstallation and ongoing maintenance costs.

In addition, because of the large number of data collection nodes, themost cost-efficient means for the WAN layer in these multi-tier networkswould be a wireless WAN. However, to avoid interference from metermodules, as well as over-complication of the data protocols, a licensedfrequency channel is typically used for the WAN, adding to the overallcost of services to the network operator. A network composed of only onewireless data collection layer would therefore be desirable,particularly if operating in the unlicensed Industrial, Scientific andMedical (ISM) band.

Yet another disadvantage of networks with distributed intelligence amongthe data collection nodes is the limited storage and processing power ofthe data collection nodes. A system that could efficiently transfer allthe raw data from the meter modules to the network's central databasewould therefore be desirable, since it would allow for more backup andarchiving options and also for more complex function calculations on theraw meter data.

The Itron patents also quote a previously developed system by Data Beam.This data collection network included few reception sites, each onecapable of handling up to tens of thousands of meters. In order to allowfor long communication range, the meter module antenna was installed ina separate (higher and/or out of building) location from the metermodule, creating significant additional cost to the meter moduleinstallation, thus significantly reducing the commercial feasibility forpractical deployment of the network. In addition, the meter module'spower consumption requirements required a mains power source orexpensive batteries, further reducing the network's commercialfeasibility.

None of the above-mentioned systems of the prior art offers a sufficientlevel of flexibility, enabling the network operator to deploy areliable, low cost, fixed data collection network, while adjusting itsinitial and ongoing costs to a wide range of application requirements,from basic daily meter reads to full two-way capabilities.Inefficiencies exist in each two-way network, in which the two-waycapability is imposed on the entire meter population, and also in eachone-way network, in which small cell configuration requires a large,unnecessary investment in infrastructure.

It is therefore desirable to introduce a simple to deploy, but highlyscalable, modular and reliable data collection system, which would offera wide range of service options, from basic metering to advancedapplications based on interval consumption data, to full two-wayapplications, while keeping the system's deployment and ongoing costsproportional to the service options and capacity requirements selectedfor various segments of the meter population.

SUMMARY OF THE INVENTION

According to a particular embodiment of the present invention, a one-waydirect sequence spread spectrum (DSSS) communications network is used asthe data collection channel (uplink) of an automatic meter reading (AMR)application and a paging network, or other suitable downlink network, isused as an optional forward (downlink) channel in a cost-effectivemanner. The network is designed to provide a cost-effective wide-areadata collection solution, i.e. capable of supporting as many meters onas large a geographical area as required by the associated meteringapplication.

The communications network includes one-way meter modules (transmitters)communicatively coupled to electric, gas and water utility meters, aswell as two-way meter modules (transceivers) coupled to such utilitymeters. The meter modules monitor, store, encode and periodicallytransmit metering data via radio signals (air messages), in anappropriate RF channel, typically within the 902-928 MHz Industrial,Scientific and Medical (ISM) band, allocated by the FederalCommunications Commission (FCC) for unlicensed operation. Metering datamessages are collected by a network of receiver Base Stations. Thereception range of each Base Station is typically over 5 miles in urbanareas, allowing sparse infrastructure deployment for a wide variety ofmetering data collection applications. The network also includes a DataOperations Center (DOC) that communicates with all the Base Stations,monitors their operation and collects metering data messages from them.The DOC may also be communicatively coupled to a paging network, orother wireless network, for sending downlink commands to the two-waymeter modules.

This invention also features a low-cost, energy efficient meter module,which provides significant benefits to the system, primarilycontributing to the long range of the wireless link, by implementing adirect sequence spread spectrum (DSSS) signal of high output power andhigh interference rejection, while consuming very low average power,thus enabling long life (many years) battery operation. The metermodule's PCB antenna is an integral part of the module. The meter moduleis simple to install, and is typically installed inside electric meters,integrated (between meter and index) in gas meters, or as an externalunit adjacent to water meters. The meter module also supports the uniqueconfiguration of the described system and limits the usage of air-timeby introducing data compression mechanisms into the wireless link.

Main advantages of the invention include:

Long wireless communication link, which provides wide-area coverage witha small number of sites (typically tens of thousands of meters in afive-mile radius per Base Station), thereby simplifying networkdeployment, reducing infrastructure initial and ongoing costs, andreducing the number of potential failure points in the network, thusincreasing reliability;

As a data collection network, the system may operate utilizing a singleRF channel, such as a spread spectrum channel within the 902-928 MHzband.

Modularity of network architecture, enabling flexibility in networkplanning, in order to optimize cost and capacity in various regionscovered by the network. A part of the network's modularity is that aforward channel, such as a paging network, can be integrated with thedata collection channel, providing a convenient transition to supplyingdata services to both one-way and two-way meter modules.

Scalability mechanisms, enabling gradual and cost-efficient increase ofinfrastructure deployment in order to meet a wide range of applicationand capacity requirements, including requirement relating to intervalconsumption data applications;

Routing of all raw metering data to the DOC central database, where itcan be easily processed, archived and accessed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating required and optional componentsof the data collection network system, according to an embodiment of thepresent invention.

FIG. 2 is a block diagram illustrating a practical configuration of atwo-way meter module.

FIG. 3 is a block diagram of a transmitter meter module.

FIG. 4 is a functional block diagram of the BPSK modulator described inFIG. 3.

FIG. 5 is a block diagram and illustration of the BPSK modulator of FIG.4.

FIG. 6 is a top and bottom drawing of the BPSK modulator of FIG. 4.

FIG. 7 is a description of the interleaving encoding, which is used bythe meter module in order to generate interval consumption data airmessages.

FIG. 8 is a description of the ‘zero current’ rotation sensor interfacelogic.

FIG. 9 is a graphic illustration of interval consumption data requiredto be transmitter in an air message.

FIG. 10 shows examples of logarithmic consumption data encoding tables.

FIG. 11 demonstrates the evaluation process by which the meter moduledetermines which consumption data-encoding table to select.

DESCRIPTION OF THE PREFERRED EMBODIMENT

General

This invention features a scalable and modular wireless fixed-base datacollection network system, comprising at least one wireless metermodule, one receiver site (Base Station) and one central site (DataOperations Center) into which all metering data is collected.

According to a particular embodiment of the present invention, a one-waydirect sequence spread spectrum (DSSS) communications network is used asthe data collection channel (uplink) of an automatic meter reading (AMR)application and a paging network, or other suitable downlink network, isused as an optional forward (downlink) channel in a cost-effectivemanner. The network is designed to provide a cost-effective wide-areadata collection solution, i.e. capable of supporting as many meters onas large a geographical area as required by the associated meteringapplication.

The communications network includes one-way meter modules (transmitters)communicatively coupled to electric, gas and water utility meters, aswell as two-way meter modules (transceivers) coupled to such utilitymeters. The meter modules monitor, store, encode and periodicallytransmit metering data via radio signals (air messages), in anappropriate RF channel, typically within the 902-928 MHz Industrial,Scientific and Medical (ISM) band, allocated by the FederalCommunications Commission (FCC) for unlicensed operation. Metering datamessages are collected by a network of receiver Base Stations. Thereception range of each Base Station is typically over 5 miles in urbanareas, allowing sparse infrastructure deployment for a wide variety ofmetering data collection applications. The network also includes a DataOperations Center (DOC) that communicates with all the Base Stations,monitors their operation and collects metering data messages from them.The DOC may also be communicatively coupled to a paging network, orother wireless network, for sending downlink commands to the two-waymeter modules.

Since transceiver power consumption is greater than transmitter powerconsumption, it is generally preferable to use transmitters where thepower source is limited. Gas and water meter modules generally have alimited power source, typically from a battery, so the meter modulesattached to such meters are generally transmitters rather thantransceivers. Electric meters can typically take their power from theelectric grid, so their power is not limited, and hence transceivers aresuitable for electric meters. However, because the cost of thetransceiver meter module is greater than the cost of the transmittermeter module, electric meters may use a transmitter to save on the endunit cost. Thus, typically gas and water meters use transmitters only,while electric meters use transmitters or transceivers according to theapplication requirements. Transceivers are used to create a two-waysystem, which has the advantage of greater capacity than a one-waysystem, and which can provide additional services (such as remoteconnect or disconnect, over-the-air programming or reprogramming ofmeter module parameters, and others) that cannot be provided by aone-way system.

Basic Network Architecture and Configuration

A high-level block diagram of a metering data collection network systemis depicted in FIG. 1. The system comprises both one-way (transmitter)meter modules 04 and two-way (transceiver) meter modules 06 coupled tometers. All meter modules are able to transmit encoded DSSS radiosignals representing metering data stored in the meter modules, such ascurrent meter reading, tamper status, meter identification data andinterval consumption data. A variety of utility meter module types(electric, gas, water) and models may operate in one metering datacollection network, utilizing the same infrastructure. Each receiverBase Station 02 is able to receive and decode DSSS encoded signals (airmessages) generated by the meter modules. The bandwidth of the DSSSsignal is approximately 2 MHz. Base Stations 02 can be optimized toreceive signals in any radio frequency range between 800 MHz and 1 GHz,including the 902-928 MHz Industrial, Scientific, and Medical (ISM) bandallocated by the FCC for unlicensed use. In a preferred embodiment, thedata collection network operates in the ISM band under the rules forunlicensed operation (Part 15 of the FCC Rules), and requires nolicensing for any portion of its wireless uplink channel.

According to the preferred embodiment, one or more Base Stations 02would be deployed to cover a geographic area. The number of BaseStations 02 needed depends on the size and type of terrain within thegeographic coverage area, as well as upon application requirements. ABase Station is typically installed at a high location (communicationtower or roof top) and consists of the following components: at leastone receiving antenna, RF cables and connectors, a DSSS receiver and acommunication interface, such as a PPP router or CDPD modem. A BaseStation may also contain a backup power source for continued operationduring a specified period of outage. Base Stations 02 receive meteringdata air messages from meter modules 04 and 06 on the uplink channel.The Base Stations decode the radio signals and relay the decodedmetering data air messages to the DOC 01. The DOC 01 is coupled to theBase Stations 02 via standard communication channels, typically by usingan IP network (such as frame relay or Internet). Other communicationmeans between the DOC and the Base Stations may be a wireless cellularnetwork, CDPD, PSTN and satellite data network. The DOC 01 consists of adatabase of all the meter modules in the network and an Internet serverfor accessing the database. This embodiment also enables the DOC toprovide alerts and event notification services via email, fax, pagerdevices and voice message generators. The DOC may be programmed toforward data directly to a user or to export files to a buffer directoryby using standard data protocols.

According to the preferred embodiment, the DOC performs metering datavalidation, processing and storage, while the Base Stations' role is todecode air messages and forward raw metering data to the DOC for centralprocessing. This structure eliminates the requirement to monitor andcontrol metering data processing tasks carried out in multiplelocations. All metering data is stored in a central location, enablingfast data access response times and equipped with suitable backupstorage means. Thus two objectives are served: low initial andmaintenance cost of Base Station hardware and software; and convenient,permanent access to all metering data collected by the network via onecentral data repository.

The DOC may be constructed, according to the application requirements tooperate in a High Availability (HA) configuration, that is two computerplatforms having the capability to transfer all processing andcommunication tasks and parameters instantaneously from one to the otherin the event of a failure of one of the platforms. In addition, the DOCmay be configured, according to the application requirements, tocommunicate with a computer platform at a remote mirror site andperiodically transfer the required data in order to maintain DisasterRecovery (DR) capability at the remote mirror site.

Network Architecture Modularity

The network's basic architecture includes transmitter meter modules,Base Stations and a DOC. However, the network is modular and may includemessage-repeating devices and, as stated, two-way meter modules and adownlink (forward) RF channel to communicate between the DOC and thetwo-way meter modules. In addition, as will be further described, thenetwork includes a variety of scalability mechanisms enablingcost-effective service in varying levels of network air-message trafficand various metering data applications.

Network Transceiver/Repeater (NTR)

According to a particular embodiment, in some cases, a cost-efficientmeans for expanding network coverage is adding NetworkTransceiver/Repeater devices (NTR) in order to provide coverage formeter modules experiencing poor or no Base Station coverage. This meansprovides more flexibility to the network operator by creating anotheroption for providing coverage to a limited geographic area. NTR cost ofdeployment and maintenance is significantly lower than that of a BaseStation. Therefore, besides being a cost effective solution to poorcoverage, it also may cost justify the enhancement of a network'scoverage to areas of low population density, thus extending the reach ofits automated metering data collection system. The deployment of NTRdevices does not require the network operator to perform any changes inany of the other elements of the network infrastructure.

In the design of a network, there will be an analysis of expected radiotraffic. Many areas will have sufficiently high radio traffic tocost-justify full Base Station coverage. However, there will be certainareas, or “holes”, in which radio traffic will be very sparse, andcannot cost-justify Base Station coverage. NTRs may provide sufficientcoverage at much lower cost. For example, a small number of meters in adeep valley may not be covered by the nearest Base Station, but do noteconomically justify the deployment of a Base Station. The NTR issmaller in size compared to a Base Station and may be mounted on a poletop, since it only needs to provide limited coverage. Therefore, itsongoing site lease cost is also significantly lower than that which anadditional Base Station would create. The use of a NTR is thus alow-cost means of covering holes in the coverage of the Base Stationnetwork, or of extending the network's coverage to areas of lowair-message traffic.

Network Transceiver/Repeater devices (NTR), shown as 03 in FIG. 1,receive metering data messages from meter models 04 and 06, decode andretransmit messages of specific meter modules. NTR devices 03 are usedin specific terrains, which endure poor radio coverage, or in otherevents of lack of coverage or of coverage degradation in a certain area.The NTR is a low cost data collection node, with lower RF sensitivityand smaller coverage (hundreds of meters) compared to a Base Station.Like the Base Station, the NTR does not perform any metering dataanalysis. It only retransmits the raw data air messages that it receivesand that are identified as received from appropriate meter moduleslisted in the NTR's memory.

The NTR 03 decodes the received air messages and then encodes andretransmits them only if the message has been received from a particularset of meter modules. Repeated messages may then be received by a BaseStation 02. Each NTR 03 retains a list of some meter modules 04, 06 thatreside in that area, and relays only messages received from those metermodules. In another embodiment, the NTR 03 checks for a NTR flag bit inthe air message that indicates whether or not to relay the message. Acombination of these two embodiments is applicable as well. Theseselective measures enable network coverage enhancement without creatingan unnecessary load of air message traffic. The NTR's selectivity allowsplanning for specific meter modules to have their air messages repeated.Also, each meter module can be programmed to use its NTR flag in orderto have only some of its air messages repeated, this way optimizing theincrease in air message traffic.

Two-Way Network

A two-way meter module is capable of transmitting metering data airmessages on demand (upon receiving an appropriate wireless command) andmay also be conveniently programmed to transmit at specific times bymaintaining a real-time clock synchronized by the wireless downlinkchannel. Two-way meter modules also receive, decode and execute othercommands such as: programming meter parameters, displaying messages oralerts on the meter's display, disconnecting and reconnecting power tothe utility meter's load. FIG. 2 depicts a block diagram of a particularembodiment of a two-way meter module, in which the elements added to aone-way meter module (transmitter described herein), in order to producea two-way meter module, include a paging receiver and decoder. The basictransmitter apparatus is described further in detail separately below.

The DOC may be coupled to a wireless downlink channel, such as a pagingnetwork, cellular network, etc., 05 through a communication link, suchas a leased line, frame relay link etc., and by using suitable standarddata protocols. The metering data collection system operates as aone-way data collection system if not coupled to a downlink channel. Thebasic one-way network may be scaled up to several higher levels ofcapacity and application features, as described herein, the highestlevel being reached by integrating a downlink channel in the system.

Network Performance Scalability

One of the key features of the system claimed herein is the ability toramp up the system's air message capacity. This feature is called“Network Performance Scalability”. In a metering data collectionapplication, various levels of message delivery probability or messageredundancy may be required, as well as various data latencyrequirements, thus affecting the amount of messages transmitted per timeperiod, i.e. air message capacity requirement. In addition, a trade-offexists between the amount of data required by the application and themaximum amount of air messages transmissions allowed, in order tomaintain air message traffic or meter module battery life at acceptablelevels. In the preferred embodiment, the network is designed so that thenetwork operator or deployment planner has the flexibility to optimizespace diversity, frequency diversity and air message duration accordingto the application requirements of delivered metering data, meter modulebattery life, metering data latency and air message deliveryprobability.

Following is a description of the levels of capacity that may beprovided, depending upon customer demand. Note that levels 2 to 4described herein may be implemented in any order.

Level 1: A sparse Base Station network is deployed, combined, ifnecessary, with NTR devices covering areas with very limited radiotraffic. This level provides adequate geographic coverage, and theminimum level of system capacity. This level is roughly defined as thecapacity required in order to provide daily reads to an urban meterpopulation. A typical urban deployment for this level would include BaseStations spaced 5 miles apart, each covering up to several tens ofthousands of meters, with few to no deployments of NTR devices.

Basic Network Control Parameters

Level 2: Space diversity is implemented to adjust network capacity, bycontrolling the amount of Base Stations used in order to providecoverage to specified meter population and metering data application ina specified geographical area. The initial phase of planning networkcoverage includes optimal selection of the number and locations of BaseStations to be deployed in the specified area. When a Base Stationcovers a large area and the meter module density or air messagefrequency requirements continuously increase, at some stage the farthestmeter modules would endure interference from the closer meter modules,and message reception probability from the farthest meter modules willdecrease. Base Stations may be added at appropriate locations in thesame geographic area, in order to increase network capacity and messagereception rate. Adding Base Stations reduces the effective range betweeneach meter module to be deployed and the Base Station closest to it, sothat more meter modules or potential meter module locations are within arange of high air-message reception probability. Thus, the placement ofadditional Base Stations in the same geographic area, without any otherchange in the network or the meter modules, will in itself increaseoverall network capacity.

Level 3: Frequency diversity is implemented by utilizing more than oneuplink frequency channel within a coverage area. Meter modules may beprogrammed to alter their transmission frequency channel each airmessage transmission. In addition, a Base Station may consist of severalreceivers in multiple frequency channels, thus significantly increasingthe Base Station's air message reception capacity. Frequency diversitymay thus eliminate or postpone coverage problems, which would otherwiserequire adding Base Station sites. In addition, frequency diversity maybe combined with space diversity by feeding receivers operating indifferent uplink frequency channels at the same Base Stations withsignals from separate antennas. In the 902-928 MHz unlicensed ISM band,a particular embodiment of the network may operate in up to 57 channels,spaced 400 kHz apart, but a more practical limit for reliable operationwould be about 10 channels. Each new frequency channel receiver added,increases the Base Station's capacity. When performed on a regional BaseStation network, adding channels significantly increases the entirenetwork's capacity.

Level 4: Another network control parameter included in the preferredembodiment consists of the direct sequence code length, which forms atrade-off with the air message's raw data bit rate parameter. In aparticular embodiment, the direct sequence chip rate is 1 Mchips/sec andthe maximum code length is 255 chips, yielding a data rate of about 4kbps. The network operator/planner may select shorter codes, namely 63,31 or 15 chips long, thus increasing the raw data bit rate. Reducingcode length reduces the signal spreading and decreases coverage rangeper Base Station, but on the other hand increases each Base Station'sair message capacity because of the shortened air messages.

Network Up-scaling by Adding a Downlink Channel

Level 5 (highest level of air-message capacity): In a one-way datacollection network, an additional, higher level of capacity may bereached by adding a downlink channel and deploying transceivers ratherthan transmitter meter modules. A two-way system has the inherentpotential to be more efficient with radio airtime resource, since fieldunits may be synchronized to a central clock, allowing transmissionaccording to allocated time slots. The higher the rate of two-way metermodules in the metered population, the higher the capacity increaseprovided by adding the downlink channel. The wireless data collectionnetwork described above may be scaled up from one-way (data collectiononly) to two-way by connecting the DOC to a wireless downlink channel ina modular way as described above. In addition, the measures described inlevels 2 to 4 above may be implemented in a two-way network as well inorder to further increase network capacity.

Integrating a downlink channel consists a cost-efficient scaling-upprocedure, which provides significant enhancement of both network airmessage capacity and metering data application functionality. Thisenhancement does not require the network operator to perform any changesin any of the already existing elements of the network infrastructure.

In a preferred embodiment of a two-way metering data network, bothone-way (transmitter) and two-way (transceiver) meter modules operate onthe same network. Transceivers can be interrogated for data at the timethat the data is required, thus eliminating the need for repeatedtransmissions, which are required in a one-way network in order tomaintain a certain level of data latency. In addition, by synchronizingall transceiver modules to one central real-time clock, a time slot fortransmission may be allocated and specified for each transceiver in acoverage area, thereby increasing the efficiency of network airtimeusage.

Although several advanced metering applications, such as demand and TOUmetering, are available from a one-way metering data collection network,two-way meter modules operating in the described two-way metering datanetwork are capable of providing additional features, including:accurate interval consumption data measurement enabled by a regularlysynchronized real-time clock, on-demand meter reading, remote disconnectand reconnect, remote programming of meter parameters and remotenotification of rate changes or other messages.

The particular embodiment of the described two-way data network enablesthe operator to mix on the same network, in a cost efficient manner, lowcost transmitters, which provide a wide range of metering datacollection features, and higher cost transceivers, which further enhancemetering data application features, while maintaining the coreadvantages of sparse infrastructure and the low cost associated withunlicensed operation of the metering data collection branch of thenetwork.

Network Application Scalability

In addition to the scalability and flexibility provided by the levels ofnetwork architecture described previously, there is another key featureof the system claimed herein, referred to as “Application Scalability”,which includes a cost-efficient method of enhancing the meteringapplications supported on the network from basic (typically daily) meterreading services to interval-consumption related applications, such asdemand analysis, load profiling and TOU rates, and further to two-waydata features. As described, some application features, includingon-demand meter reading, remote disconnect and reconnect, remoteprogramming of meter parameters and remote notification of rate changesor other messages, require that the network architecture be scaled up toa two-way network by adding a downlink channel. However, applicationsbased on interval consumption data can operate successfully on a one-waynetwork and, by using the method described herein, a relatively minorincrement in air message traffic is incurred.

In prior art, extensive infrastructure is deployed in order to collectinterval consumption data frequently (e.g. every 15 minutes). However,in many cases, particularly in residential metering applications,consumption data may be required in high resolution, but some latency ispermitted in data availability. For example, fifteen-minute demandanalysis could be required, but may be performed each morning on datacollected the previous night, allowing several hours in order to collectthe required interval consumption data. It would therefore be beneficialfor the network service provider to have the flexibility to deployinfrastructure appropriate to the application and invest in additionalinfrastructure for high-end applications, such as on-demand reads, onlyin proportion to the meter population for which it is required.

In a particular embodiment, an interval consumption data messageincludes an array of interval consumption values, each one representingthe consumption increment of one interval. In order to reduce the totallength of air messages, or the total number of fixed-length intervaldata air messages, a method referred to as “logarithmic table encoding”of consumption values is used, which encodes interval consumption datain the air message. It is a method to map the range of consumptionvalues into a more limited number of values, for the purpose of reducingthe number of bits of information transmitted over the air. This mappingis executed by a series of tables, which have been predefined by thecustomer, according to the expected dynamic range of the intervalconsumption.

FIG. 9 shows an example of interval consumption data that may berequired by a demand analysis application. In this example, it isassumed that an accuracy of 0.1 kWh is sufficient. Also by way ofexample, a 12 hour total time period is measured for 15 minuteconsumption data. In order to optimize the consumption profilereconstructed, the total time period may be divided to severalsub-periods, in this example, 3 periods of 4 hours. The flexibility ofassigning different encoding tables to different sub-periods reduces thestatistical error of the decoded consumption profile compared to theactual one.

The numeric consumption values given in FIG. 9 would traditionallyrequire an encoding table with values ranging from zero to 1800 Wh, in100 Wh increments, i.e. 19 values, requiring 5 bits per each consumptioninterval to encode. In order to reduce the overall air message trafficassociated with interval consumption data applications, only 2 bits areused in this example for interval consumption encoding. Thisapproximation inevitably creates an error in the reconstruction of aconsumption profile compared to the actual consumption, but withappropriate definition of a set of encoding tables for the meter moduleto use, an acceptable error level may be reached.

The set of tables assigned to a meter module may differ from one metermodule to another according to the expected consumption patterns. TheDOC maintains a bank of available tables from which a set of tables isdefined for each meter module during installation. An example of such aset of encoding tables is shown in FIG. 10.

An interval consumption air message in the provided example wouldtherefore contain 2 bit interval data for 48 intervals of 15 minutes,i.e. 96 bits, plus two bits identifying the table chosen per eachperiod, to a total of 102 bits, compared to 19 bits×48 intervals, or 912bits, in a traditional system with no logarithmic encoding.

The meter module selects an encoding table by building a consumptionprofile with each of the tables stored in its memory, and comparing itto the actual profile, stored in its memory as a series of actualreading values. Then the meter module applies a criterion by which toselect the best table, e.g. the table that yields the lowest maximumerror during the metered period, or the lowest variance between theencoded and actual profile.

The encoded consumption profile is built in the following process: ifduring an interval, actual (aggregated) consumption reached a value X,the interval consumption value, which would bring the encodedconsumption profile to the closest value less or equal X, and which isalso represented by a two-bit code in the encoding table, is used inorder to build the encoded consumption profile. An example illustrationof the profiles constructed vs the actual consumption is shown in FIG.11. In the example, if a minimum error criterion is applied for the 6-10four-hour period shown, then Table 3 would be chosen, as it yields amaximum error of 200 Wh (0.2 kWh) during the period. A table is selectedfor the other two periods in the example (10-14, 14-18) in an identicalprocess. A reverse process is applied at the DOC in order to extract theinterval consumption data, in which the table set used by the metermodule is retrieved and then the consumption profile is reconstructedfor each sub-period.

In order to provide a high level of redundancy of interval consumptiondata, another data encoding method is provided, referred to as intervalconsumption data “interleaving air message encoding”, which splitsinterval consumption values between separate messages. In a particularembodiment, depicted graphically in FIG. 7, three separate intervalconsumption data air messages are transmitted that relate to the sameconsumption period b−a. The first air message includes samples taken attimes a, a+x, a+2x, . . . b. The second air message includes samplestaken at times a+x/3, a+4x/3, a+7x/3, . . . b+x/3. The third air messageincludes samples taken at times a+2x/3, a+5x/3, a+8x/3, . . . b+2x/3.Two bits identifying the reference time are appended to the intervalconsumption data air message described above (to a total of 104),enabling the DOC to correctly correlate different interval consumptionair messages received from the same meter module.

Interval consumption data is defined to have a resolution valuecorresponding to the size of the time interval between consecutiveconsumption values sampled. If a message is lost, interval consumptiondata is still available at the DOC with a resolution of x or better. Ifno messages are lost, interval data is provided at the DOC with aresolution of x/3. This way, the meter module maintains the potential toprovide high resolution interval consumption data, but also provideslower resolution interval consumption data with a higher redundancylevel than that available when data is not split as described above.

By combining the two encoding methods described, a highly reliable andefficient interval consumption data collection system is provided. Inthe example of FIG. 9, 8 daily messages (typical length about 100 bits)are required to deliver interval data, with a redundancy level of 3,whereas without using the provided methods, at least 14 daily messageswould be required to achieve the same redundancy level. The encodingmethods provided therefore maintain high channel reliability whileincreasing network capacity, by 75% in this example.

The system supports interval consumption data applications even when apower outage occurs. This is performed by appropriate utilization of themeter module non-volatile memory, and without requiring any backupbattery. Following is described a method, combined with the methodsdescribed above for data encoding, for retrieving interval consumptiondata in a one-way data collection network, after an outage event hasoccurred.

The meter module periodically and frequently executes a procedure, whichupdates and stores an interval consumption data message. The purpose ofthis process is to prevent from losing interval consumption data upon anoutage event.

A general distinction exists in the system between a regular meteringdata air message, referred to as “full data message”, and an intervalconsumption data air message, which includes only a series ofconsumption data values, as sampled by the meter module. Upon powerrestoration after outage, the meter module transmits a full datamessage, also including a flag signifying that power has just beenrestored. In parallel, a new interval consumption data cycle (period)begins as the module's microcontroller wakes up. Shortly thereafter, thelast saved interval consumption data air message is transmitted. Themeter module maintains an internal flag called ‘first intervalconsumption message transmitted’. Only once this flag is set, can theprocedure that updates and stores an interval consumption data messageoperate. The flag is reset upon power restoration, and set once the lastsaved interval consumption message is transmitted. The DOC identifiesthe power restoration message and thus identifies the intervalconsumption message that follows it as the last saved intervalconsumption message to follow, enabling the DOC to reconstruct intervalconsumption data prior to the outage event. In addition, the nextscheduled full data message, following the power restoration message, isalso flagged by the meter module as the ‘second full data message sincepower restored’. This acts as a redundant measure to identify the lastsaved interval consumption message before the outage event.

Meter Module

Following is a description of the meter module apparatus used in thenetwork system. The meter module described has unique features of lowoverall power consumption, high output power and low cost overalldesign, enabling long battery life and long communication range in acommercially feasible fixed wireless network for a variety of meteringapplications.

Each meter module in the network continuously monitors the resourceconsumption according to an input sensor that is coupled to the utilitymeter. In a particular embodiment, the meter module may be integratedinside, or as a part of, the meter enclosure. The meter module storesand transmits a wide array of data fields related to the meter,including consumption data, meter identification and calculation factordata, and various status alerts. Meter reading is stored as anaggregated value and not as an increment value, thus maintaining thereading value's integrity if an air message is not received at the DOC.A one-way meter module transmits a metering data air message once everypreprogrammed time interval. A block diagram of the transmitter isdepicted in FIG. 3 according to a particular embodiment of the presentinvention. In this particular implementation, the transmitter includes ameter interface logic module 50 that collects consumption, tamper statusand other data from an associated utility meter 51. It should be notedthat, although FIG. 3 depicts a single meter interface module forpurposes of simplification, multiple meter interface logic modules maybe used in a single transmitter to interface with more than one utilitymeter. The meter interface logic module 51 operates continuously anddraws only a small amount of current. It includes several standardsensors, such as magnetic reed switches or optical sensors in order totrack consumption, tilt sensors for tamper detection and voltage sensorsto determine outage or power restoration events.

The transmitter includes a serial data communication interface 20, whichis used for testing and initialization at the shop or in the field byusing a short-range wireless magnetic loop interface or a PC with aserial data port. The wake-up circuit 40 is designed in order to savepower, particularly in battery operated transmitters, by keeping thecontroller 60, RF module 70, DSSS encoder 80 and LPF 85 in a turned off(no power) state, which is interrupted only if an event was triggered bythe meter via the meter interface logic 50, by an external device viathe serial data interface 20, or by the timer completing its timingcycle and triggering a wake-up signal. In another embodiment,particularly with an unlimited power source as may be the case withelectric meters, the controller operates continuously and also maintainsa timer, and a wake-up circuit is not used.

If an event occurred which is determined by the controller 60 to triggerair message transmission, the controller module 60 prepares a datapacket, which is converted to a direct sequence (PN code generation andsignal spreading) by the DSSS encoder 80. The spread signal is filteredby a low pass filter (LPF) 85 and is the used as the modulating signalfor the BPSK modulator. The RF module 70 includes a synthesizercontrolled local oscillator (LO) 71, a Binary-Phase-Shift-Keying (BPSK)modulator 73 and a power amplifier (PA) 75. The power amplifier 75produces up to 1 W of power for output to an on-board printed antenna76. Once the controller has handled the event that woke it up from itspower-down mode, whether an air message transmission or other task wasperformed, it returns to its power-down (idle) mode.

Restrained Power Supply

In a particular embodiment of the meter module, a restrained powersupply 10 is implemented in the meter module, which is essential inorder to maintain an acceptable level of radio interference in the eventof uncontrolled transmission by a malfunctioning meter module. Onesource of danger in the system is the possibility that a transmitterwill malfunction and begin transmitting continuously. The result may bethat the entire frequency channel would be blocked in that coverage areaduring the time of transmission, until the transmitter's power sourcedies (and this would continue indefinitely if the power source isunlimited, such as an electric grid). Although this event is highlyunlikely, measures have been designed into the system to prevent it fromhappening. In the meter module described herein, a cost effectivemechanism has been introduced to prevent an uncontrolled transmissionfrom blocking network air message traffic. This mechanism provides twoadditional benefits to the system: high output power with a limitedpower source and an immediate outage notification feature, also known asa ‘last gasp’ transmission.

The meter module's power supply hardware is designed to prevent thedescribed phenomenon of continuous uncontrolled transmission. Twospecific physical limits have been designed into the meter module tomeet this purpose. A capacitive element and a limited current source arecombined in the meter module's power supply. The capacitive element isused as a buffer stage between the energy source and the load. Thecapacitive element stores sufficient energy, as required for ahigh-power air message transmission. Due to its inherent physicallimitations, the capacitive element can deliver sufficient power fortransmission but only for a limited period of time. Since the durationof transmission is relative to the element's physical capacitance, andphysical capacitance is related to the size of the element, the size ofthe capacitive element is selected to be big enough to deliver enoughenergy for a complete transmission session, but not more than that. Thisway, the maximum potential blockage duration due to unwantedtransmission is restricted to one transmission session. In addition, thelimited current source imposes a physical limitation on the rechargetime required for the capacitive element to reach the required energylevel for another air message transmission, thus limiting the on-offtransmission duty cycle to a level that is harmless in terms of networkcapacity. In a particular embodiment, the transmitted power is one watt,for a duration of 150 msec and with a recharge time of 90 seconds. Thistranslates to a maximum of 960 messages per day, which is about 1% of anestimated channel capacity of 86,400 messages per day. Since networkcoverage is designed with a much higher safety margin than 1%, amalfunctioning transmitter would not be destructive to the networkoperation, allowing sufficient time for software means to detect andidentify the source of the problem.

The described power supply therefore also enables the transmitter togenerate high-power air message transmissions, even with a power sourcethat supports a very low current drain. It also enables an enhancementof electric metering applications by enabling a ‘last gasp’ meteringdata air message transmission when an outage event is detected by anelectric meter module.

Low Power Rotation Sensor Circuit

In a particular embodiment of the meter module, appropriate circuitryand controller logic enable near zero power consumption of the rotationsensing mechanism, which is a part of the meter interface logic 50. Thismay be a decisive factor in the expected operating life of a metermodule powered by a limited power source such as a battery.

A typical prior art sensor configuration appears in FIG. 8A. The switchhas two operation states, open and closed. When the switch is open thecurrent circuit is broken and the voltage measured at the V-sense nodeequals the supply voltage Vcc. When the switch is closed the voltagemeasured at V-sense node is the circuit's ground level reference voltagei.e. zero voltage. Distinguishing between the two electrical states atthe V-sense node allows distinguishing between the two switch statesopen and closed.

Although most switches have finite conductivity, typical powerconsumption in the open state is acceptable for long operating life.However, during the closed state, power is consumed at a level that maybe significant when the energy source is limited as in battery-powereddevices, and when that limited source must operate for lengthy periodsof time, such as is the case with meter modules. In addition, the amountof energy wasted typically cannot be predicted, and may vary widely withutility customer consumption patterns.

An alternative to the standard sensor configuration may be referred toas “Zero Current Sensors Configuration”. The implementation is basedupon a component selection and geometrical arrangement of two sensors,such that at any possible position of the sensed rotating element, suchas a magnet or a light reflector, only one of the two sensors may betriggering a closed switch state.

FIG. 8B illustrates the solution. The two switch circuits are activatedor deactivated by control commands of the controller 60. Loading highstate voltage into a register causes the activation of the associatedswitch. Loading low state voltage into a register causes deactivation ofa switch. When a switch is deactivated, no current can flow via theswitch, even when the switch state is close and of course, no currentflows when the switch is open. The result is that no current flows, andhence no energy is wasted, when the switch is open, or if the switch isde-activated without regard to the state of the switch.

The controller module 60 is programmed to deactivate a sensor circuitimmediately once that sensor has been detected in a closed switch state.In addition, the controller module activates the other sensor circuit.For example, if the initial state was that Switch 1 is activated andSwitch 1 is projected by the projection element (magnet/reflector), itchanges its state from open to close, the voltage at V-sense 1 ischanged from high state voltage to zero. The voltage drop wakes up thecontroller module 60, which then deactivates Switch 1 and activatesSwitch 2. Since Switch 2 is located in different projection zone thanSwitch 1, Switch 2's state when activated is open so no current flowsvia Switch 2. Since Switch 1 is now de-activated, no current flows viaSwitch 1 either. When the rotation of disk or wheel continues and theprojection element reaches the projection zone of Switch 2, Switch 2changes its state from open to close, the V-sense 2 is changed from highstate voltage to zero, the controller unit 60 is woken up, and thecontroller unit 60 then immediately deactivates Switch 2 and activatesSwitch 1. One rotation of the disk or wheel is defined as state changeof Switch 1 from open to close followed by state change of Switch 2 fromopen to close, after which the controller increments the meterrevolution count. However, neither switch is ever active and closed.Therefore the continuous current drain of the sensor circuitry onlyincludes that of the open switch, which is near zero.

Low Cost RF Modulator

FIG. 4 is a block diagram depicting an example arrangement forimplementing the BPSK modulator 73 of FIG. 3. Unlike conventionalmicrowave monolithic integrated circuit (MMIC) BPSK modulators, whichare large and expensive, the arrangement illustrated in FIG. 4 iscompact and can be implemented at a low cost. The BPSK modulator of thepresent invention includes a diode bridge 1202 that can be switched toprovide either an in-phase output signal (upper configuration of FIG. 4)or an inverted-phase output signal (lower configuration of FIG. 4).Balun (balance/unbalance) circuits 1201, implemented as 180° powerdividers, are used at the inputs and outputs of the diode bridge 1202.The balun circuit 1201 at the input of the diode bridge 1202 feeds thecross switch implemented by the diode bridge 1202, and the balun circuit1201 at the output of the diode bridge 1202 sums the energy either inphase or in inverted phase. The balun circuits 1201 are implementedusing an FR4-type printed circuit board (PCB), avoiding the need fortuning during production. The PCB has four layers, the inner two ofwhich are used to implement the balun circuits 1201. Each balun circuit1201 includes three broadside coupled transmission line pairs.

FIG. 5 is a schematic diagram illustrating the arrangement of FIG. 4 ingreater detail. Diodes 5A, 5B, 6A and 6B form the diode bridge 1202. Aninput balun 1201 is formed by three pairs of coupled transmission lines,namely, transmission lines 1A and 1B, transmission lines 2A and 2B, andtransmission lines 3A and 3B. Similarly, an output balun 1201 is alsoformed by three pairs of coupled transmission lines: transmission lines10A and 10B, transmission lines 11A and 11B, and transmission lines 12Aand 12B. The input balun 1201 feeds the diode pair formed by diodes 5Aand 5B and the diode pair formed by diodes 6A and 6B with antipodalsignals that are approximately 180° apart in phase. The modulationprovided through the baseband signal bi-phase modulates each branch. Theoutput balun 1201 sums the two branches. Small transmission lines 4 and9 provide small corrections to ensure that the two branches are 180°apart in phase.

FIG. 6 is a cross-sectional diagram depicting an example physicalimplementation of the arrangement of FIG. 5. The modulator isimplemented using a PCB made of FR4-type material. The PCB has fourlayers and is surrounded by a shield. For 1 MHz modulation, themodulator measures 15 mm by 23 mm and has a bandwidth of 750-1500 MHz.Half octave phase accuracy is within 1°, and full octave phase accuracyis within 2.5°. Amplitude imbalance is preferably less than 0.2 dB, andsignal loss is preferably less than 6 dB. Carrier suppression ispreferably at least 17 dB.

1. A wireless network system for wide-area metering data collection, thenetwork system comprising: two or more meter modules configured tomonitor, store, encode and periodically transmit, via radio signals,metering data collected at a predetermined consumption interval; atleast one receiver base station configured to receive, decode, store andforward the metering data to a data operations center (DOC) acting as acentral database and a metering data gateway; the DOC configured toprocess, validate, and store metering data in a meter databasemaintained for every meter module in the network, wherein each of themeter modules collects the metering data for a consumption periodcomprised of a plurality of consumption intervals and encodes themetering data by using a logarithmic table to compress the metering dataand reduce the number of bits needed for transmission, and the DOCmaintains sets of logarithmic encoding tables, each set of the encodingtables corresponding to a different consumption interval pattern, andmaintains a registry specifying a subset of encoding tables assigned toeach of the meter modules.
 2. The network system according to claim 1,wherein each meter module selects an encoding table from the assignedset of encoding tables based on a comparison of a consumption profileassociated with each of the set of encoding tables and an actualconsumption profile.
 3. The network system according to claim 1, whereina number of base stations, a number of reception frequency channels, andmeter module message bit rate are adjusted based on required messagedelivery probability and metering data latency, and available metermodule battery life.
 4. The network system according to claim 1, furthercomprising a network transceiver/repeater (NTR) device configured torepeat a message received from a meter module based on a moduleidentification number of the meter module or on a flag in the messagereceived from the meter module.
 5. The network system according to claim1, wherein each of the meter modules is further configured to interleavelower resolution overlapping subsets of the encoded metering datacollected for the consumption period to generate a plurality oftransmitted messages for each consumption period.
 6. A meter moduleconfigured to operate in the network system of claim 1, the meter modulecomprising: a rotation detector to detect rotation of a meter dial as anindication of usage; a data storage; a data processor; and a directsequence spread spectrum transmitter and an antenna, wherein therotation detector, the data storage, the data processor, and thetransmitter and the antenna are all within the same physical enclosure.7. The meter module according to claim 6, wherein the enclosure iscomprised inside the enclosure of an electric meter.
 8. The meter moduleaccording to claim 6, wherein the enclosure is disposed between a gasmeter and a gas meter index.
 9. The meter module according to claim 6,wherein the transmitter transmits radio signals at an output powerbetween 0.5 and 1 Watt.
 10. The meter module according to claim 6,further comprising a power supply to the transmitter including acapacitive element and a limited current source, in combination, whichsupply power to the transmitter to transmit radio signals with outputpower above a predetermined threshold during a short transmission burstinitiated at a start of a power outage to notify of the power outage.11. The meter module according to claim 6, the rotation detectorcomprising two sensors, each sensor including a switch that opens andcloses to indicate rotation of the meter dial to a predeterminedposition, and a controller, wherein based on the physical arrangement ofthe two sensors and on the controller controlling the switch of eachsensor, the two sensors of the rotation detector draw near zero current.12. The meter module according to claim 6, further comprising an outagerecovery system configured to perform notification of a power outage,notification of power restoration, storage of metering data, andtransmission, after power restoration, of any stored metering datacollected prior to a power outage and not previously transmitted.